1. Field of the Invention
The present invention relates to a lithographic apparatus and, in particular, to wireless signaling for a lithographic apparatus.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning devices, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist).
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In order to obtain an accurate projection of the pattern onto the substrate, different requirements have to be met inside a lithographic apparatus. As an example, accurate displacement and positioning of both the substrate and the patterning devices are required, the environmental conditions inside the lithographic apparatus have to be monitored and maintained to meet the requirements. In order to obtain these requirements, the lithographic apparatus is equipped with a plurality of instruments such as sensors, actuators, pumps, etc. . . . In most cases, those instruments are wired to either a power supply and/or a control unit by cables or wires. Examples of such cables are optical fibers and electrically conductive wires provided with an insulation layer.
Due to an increased complexity of the lithographic apparatus, the number of wires and cables required for providing power to those instruments and for transporting information between those instruments and the control unit increases. These wires and cables may cause a number of problems inside the lithographic apparatus.
A further drawback of the application of wires and cables is that they are a potential source of contamination. The lithographic process usually takes place in a highly purified environment. As a particular example, this environment may be a vacuum environment. In case conventional cables or wires are used in such environments, outgassing of the insulation material surrounding the electrically conductive wire may occur. This outgassing may adversely affect the lithographic process.
An other drawback of the application of wires or cables is that it may reduce the reliability of the lithographic apparatus. The connectors connecting the instruments, the control unit or the power supply with the cable or wire may fail due to repetitive movement of the cable or wire. The wire or cable may also be damaged due to mechanical stresses.